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A new study by Batygyin and Laughlin suggest that a Jupiter migration toward the inner region of the Solar System during the early stages of system formation cleared the habitable region (Goldilocks zone) around the Sun from early planets that too large and with atmospheres too dense to support life. As they put it:

Jupiter migrates inward from a > 5 astronomical units (AU) to a ≈ 1.5 AU before reversing direction, can explain the low overall mass of the Solar System’s terrestrial planets.

They propose this scenario to explain the differences between the Solar System and other planetary systems in which large planets are found in the proximity of the starts.

Among the many questions I have: How is it physically possible for such a migration to occur? Is there a way to verify the migration hypothesis with observations? How different would have been the hypothetical planets in the area currently occupied by Earth? If such a migration toward the Sun started, what prevented Jupiter from continuing inward and collapsing with the Sun? Is it possible for such a migration to occur again?

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    $\begingroup$ Maybe read scholarpedia.org/article/Planetary_migration as a knowledge-basis... $\endgroup$
    – AtmosphericPrisonEscape
    Mar 25, 2015 at 16:03
  • $\begingroup$ Thanks, @AtmosphericPrisonEscape! That is a fantastic point to start. $\endgroup$
    – arkaia
    Mar 25, 2015 at 16:13
  • $\begingroup$ Yeah, I think so. Also the guy who wrote it (Armitage) is really famous inside the planetary community, so he's a credible source ;) Also the scenario you're looking for is referred to as 'Grand tack'-modell. Sorry I'm just too lazy to write an answer. $\endgroup$
    – AtmosphericPrisonEscape
    Mar 25, 2015 at 18:13
  • $\begingroup$ Several weeks ago there a TV documentary on here which explained all of that. Some astronomers began to question the history of our solar system when gas giant exo-planets were found in very close orbits to nearby stars. Jupiter's move to a close orbit of the Sun took in much of the material for creating rocky planets; it's why Mars is so small compared to Earth & Venus. The formation of Saturn & its movements is what forced Jupiter to its current location. $\endgroup$
    – Fred
    Mar 26, 2015 at 1:10

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Did Jupiter really make Earth (in)habitable?

Perhaps, but it's tough to tell.

I wrote up an answer for a question on Physics getting at some more specific issues here; bear with me if I re-use a little bit of it.

How is it physically possible for such a migration to occur?

Planetary migration in the Solar System is described by the Nice Model (or, actually, the Nice II Model, its successor). Basically, the gas giants started out at different orbital semi-major axes than they are in today. There is one change in order, though: Neptune is closer in than Uranus (making the order Jupiter, Saturn, Neptune, Uranus). Also, there may have been a 5th giant (actually an ice giant), which was subsequently ejected. It would have been similar to Uranus and Neptune in composition and size.

Here's a quick summary of the Nice Model:

  1. Planetesimals and Kuiper Belt Objects interact with the giants, moving Jupiter inwards a tad and the other three (or four) outwards.
  2. Eventually, resonances come into play. These are ratios between orbital periods. Jupiter and Saturn cross a mutual threshold.
  3. Saturn moves outward and Jupiter moves inward. A chain of events happens, where Neptune and Uranus are dramatically moved outwards, with Neptune being chucked to the rear (and the hypothetical 5th giant being ejected). You can watch the video given in that question here.

Here are the before and after pictures, stolen borrowed from that question:

enter image description here

enter image description here

I can, specifically, recommend the papers I mentioned there: Fassett & Minton (2013), Deienno & Nesvorny (2014), Brasser et al. (2009), Nesvorny (2011), Nesvorny & Morbidelli (2012), and Gomes, Levison, Tsiganis and Morbidelli (2005) - in no particular order, I think.

Is there a way to verify the migration hypothesis with observations?

Well, simulations were used in some of the mentioned papers, especially in those co-authored by Nesvorny, who was involved in recent developments of the Nice Model. These lead to the hypothetical 5th giant, because in some cases, it is necessary as a sort of sacrificial lamb, to prevent Uranus or Neptune from being flung out.

We really can't observe this happening in real time, so simulations are our best shot.

How different would have been the hypothetical planets in the area currently occupied by Earth?

The Late Heavy Bombardment might not have happened. That's a whole avenue of investigation into alternative astronomical history. It would involve fewer craters and possibly less fewer small collisions between some objects. It would be a calmer place. No migration = no LHB.

Beyond that, it's hard for anyone to say. Detailed simulations are really difficult, because the exact conditions that matter - not just orbital positions - are hard to model.

If such a migration toward the Sun started, what prevented Jupiter from continuing inward and collapsing with the Sun?

There just wasn't enough impetus from the encounter with Saturn to fling it inwards. A migration isn't just a planet rushing willy-nilly into space; it's a delicate system of slight orbital changes. All odds were against something like this happening.

Is it possible for such a migration to occur again?

Only if the right resonances appear, which is unlikely.

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